Enums: specify base

Change-Id: I540435869bfd22b47eaa4f2f1471654c53707ea1
Reviewed-on: https://skia-review.googlesource.com/c/168279
Commit-Queue: Cary Clark <caryclark@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
4 files changed